[Backport 8.15] Add hits_time_in_millis and misses_time_in_millis to enrich stats (#2845) (#2848)

* Add hits_time_in_millis and misses_time_in_millis to enrich stats

* Switch to DurationValue<UnitMillis>

(cherry picked from commit ce74e92)

Author: pquentin

output/openapi/elasticsearch-openapi.json

@@ -20,6 +20,7 @@
 import { TaskInfo } from '@tasks/_types/TaskInfo'
 import { Id, Name } from '@_types/common'
 import { integer, long } from '@_types/Numeric'
+import { DurationValue, UnitMillis } from '@_types/Time'
 
 export class ExecutingPolicy {
   name: Name
@@ -38,6 +39,10 @@ export class CacheStats {
   node_id: Id
   count: integer
   hits: integer
+  /* The amount of time in milliseconds spent fetching data from the cache on successful cache hits only. */
+  hits_time_in_millis: DurationValue<UnitMillis>
   misses: integer
+  /* The amount of time in milliseconds spent fetching data from the enrich index and updating the cache, on cache misses only. */
+  misses_time_in_millis: DurationValue<UnitMillis>
   evictions: integer
 }